\begin{tikzpicture}
    \tkzDefPoints{0/0/O}
    \tkzDefPoint(180:1.5){A}
    \tkzDefPoint(0:1.5){B}
    \tkzDefPoint(70:1.5){C}

    \tkzDrawCircle[thick](O,A)
    \tkzDrawSegments(A,B)
    \tkzDrawSegments(A,C  B,C  O,C)
    \tkzDrawPoint(O)
    \tkzMarkRightAngle(A,C,B)
    \tkzLabelPoints[below](O)
    \tkzLabelPoints[left](A)
    \tkzLabelPoints[right](B)
    \tkzLabelPoints[above](C)
\end{tikzpicture}

